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Aspects of autonomous corner modules as an enabler for new vehicle chassis solutions
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
2006 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis adopts a novel approach to propelling and controlling the dynamics of a vehicle by using autonomous corner modules (ACM). This configuration is characterised by vehicle controlled functions and distributed actuation and offers active and individual control of steering, camber, propulsion/braking and vertical load.

Algorithms which control vehicles with ACMs from a state-space trajectory description are reviewed and further developed. This principle involves force allocation, where forces to each tyre are distributed within their limitations. One force allocation procedure proposed and used is based on a constrained, linear, least-square optimisation, where cost functions are used to favour solutions directed to specific attributes.

The ACM configuration reduces tyre force constraints, due to lessen estrictions in wheel kinematics compared to conventional vehicles. Thus, the tyres can generate forces considerably differently, which in turn, enables a new motion pattern. This is used to control vehicle slip and vehicle yaw independently. The ACM shows one important potential; the extraordinary ability to ensure vehicle stability. This is feasible firstly due to closed-loop control of a large number of available actuators and secondly due to better use of adhesion potential. The ability to ensure vehicle stability was demonstrated by creating actuator faults.

This thesis also offers an insight in ACM actuators and their interaction, as a result of the force allocation procedure.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , viii, 22 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2006:101
National Category
Vehicle Engineering
Identifiers
URN: urn:nbn:se:kth:diva-4275ISBN: 978-91-7178-559-6 (print)OAI: oai:DiVA.org:kth-4275DiVA: diva2:11577
Presentation
2007-02-22, Sal D41, KTH, Lindstedtsvägen 17, Stockholm, 13:00
Opponent
Supervisors
Note
QC 20101117Available from: 2007-02-14 Created: 2007-02-14 Last updated: 2010-11-17Bibliographically approved
List of papers
1. Autonomous corner modules as an enabler for new vehicle chassis solutions
Open this publication in new window or tab >>Autonomous corner modules as an enabler for new vehicle chassis solutions
2006 (English)In: FISTA TransactionArticle in journal (Refereed) Published
Abstract [en]

Demands for new functions and refined attributes in vehicle dynamics are leading to more complex and more expensive chassis design. To overcome this, there has been increasing interest in a novel chassis design that could be reused in the development process for new vehicle platforms and mainly allow functions to be regulated by software. The Autonomous Corner Module (ACM) was invented at Volvo Car Corporation (VCC) in 1998. The invention is based upon actively controlled functions and distributed actuation. The main idea is that the ACM should enable individual control of the functions of each wheel; propulsion/braking, alignment/steering and vertical wheel load. This is done by using hubmotors and by replacing the lower control arm of a suspension with two linear actuators, allowing them to control steering and camber simultaneously. Along with active spring/damper and wheel motors, these modules are able to individually control each wheel's steering, camber, suspension and spin velocity. This provides the opportunity to replace mechanical drive, braking, steering and suspension with distributed wheel functions which, in turn, enable new vehicle architecture and design.

The aim of this paper is to present the vehicle dynamic potential of the ACM solution, by describing its possible uses and relating them to previous research findings. Associated work suggests chassis solutions where different fractions of the functions of the ACM capability have been used to achieve benefits in vehicle dynamics. For instance, ideas on how to use active camber control have been presented. Other studies have reported well-known advantages, such as, good transient yaw control from in-wheel motor propulsion and stable chassis behaviour from four-wheel steering, when affected by side wind. However, this technology also presents challenges. One example is how to control the relatively large unsprung mass that occurs due to the extra weight from the in-wheel motor. The negative influence from this source can be reduced by using active control of vertical forces. The implementation of ACM, or similar technologies, requires a well-structured hierarchy and control strategy. Associated work suggests methods for chassis control, where tyre forces can be individually distributed from a vehicle path description. The associated work predominately indicates that the ACM introduces new opportunities and shows itself to be a promising enabler for vehicle dynamic functions.

Keyword
Chassis control, vehicle dynamics, steering, propulsion, active suspension
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-6769 (URN)
Note
QC 20100721Available from: 2007-02-14 Created: 2007-02-14 Last updated: 2010-07-21Bibliographically approved
2. Stability of an electric vehicle with permanent magnet in-wheel motors during electrical faults
Open this publication in new window or tab >>Stability of an electric vehicle with permanent magnet in-wheel motors during electrical faults
2007 (English)In: World Electric Vehicle Journal, ISSN 2032-6653, E-ISSN 2032-6653, Vol. 1, 100-107 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents an analysis of the stability of an electric vehicle equipped with in-wheel motors of permanent-magnet type during a class of electrical faults. Due to the constant excitation from the permanent magnets, the output torque from a faulted wheel cannot easily be removed if an inverter shuts down, which directly affects the vehicle stability. In this paper, the impact of an electrical fault during two driving scenarios is investigated by simulations; using parameters from a 30 kW in-wheel motor and experimentally obtained tire data. It is shown that the electrical fault risks to seriously degrading the vehicle stability if the correct counteraction is not taken quickly. However, it is also demonstrated that vehicle stability during an electrical fault can be maintained with only minor lateral displacements when a closed-loop path controller and a simple method to allocate the individual tire forces are used. This inherent capacity to handle an important class of electrical faults is attractive; especially since no additional fault-handling strategy or hardware is needed.

Keyword
control system, electrical failure, inverter, in-wheel motor
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-6770 (URN)2-s2.0-70849121041 (Scopus ID)
Note

QC 20100721

Available from: 2007-02-14 Created: 2007-02-14 Last updated: 2017-12-14Bibliographically approved
3. Control of electric vehicles with autonomous corner modules: implementation aspects and fault handling
Open this publication in new window or tab >>Control of electric vehicles with autonomous corner modules: implementation aspects and fault handling
2008 (English)In: International Journal of Vehicle Systems Modelling and Testing, ISSN 1745-6436, Vol. 3, no 3, 213-228 p.Article in journal (Refereed) Published
Abstract [en]

In this paper, vehicle dynamics for electric vehicles equipped with in-wheel motors and individual steering actuators are studied adopting the principles of optimal tyre-force allocation. A simple method for describing the constraints owing to tyre and actuator limitations is described. The control architecture is evaluated by investigating its response to realistic fault conditions. The evaluation demonstrates that the control architecture's ability to ensure vehicle stability generally is good. However, during major faults and extreme driving situations, vehicle stability is not maintained unless the constraints in the optimisation process used for tyre-force allocation are adapted to the specific fault.

Keyword
ACM; Adhesion potential; Autonomous corner module; Electric in-wheel motor; Electric vehicle; Fault handling; Force allocation; Tyre constraints; Vehicle control; Vehicle dynamics
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-6771 (URN)10.1504/IJVSMT.2008.023839 (DOI)2-s2.0-63149174243 (Scopus ID)
Note

QC 20100721

Available from: 2007-02-14 Created: 2007-02-14 Last updated: 2013-12-04Bibliographically approved
4. Exploiting autonomous corner modules to resolve force constraints in the tyre contact patch
Open this publication in new window or tab >>Exploiting autonomous corner modules to resolve force constraints in the tyre contact patch
2008 (English)In: Vehicle System Dynamics, ISSN 0042-3114, E-ISSN 1744-5159, Vol. 46, no 7, 553-573 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents a general force allocation strategy for over-actuated vehicles, utilising technologies where tyre forces can be more freely controlled than in conventional vehicles. For the purpose of illustration, this strategy has been applied and evaluated using a design proposal of an autonomous corner module (ACM) chassis during a transient open-loop response test. In this work, the vehicle has been forced to follow a trajectory, identical to the performance of a conventional front-steered vehicle during the manoeuvre studied. An optimisation process of tyre force allocation has been adopted along with tyre force constraints and cost functions to favour a desired solution. The vehicle response has been evaluated as open-loop, where tyre forces are shown to be allocated in a different manner than in conventional front-steered vehicles. A suggested approach for a control scheme of steering actuators is presented, where the actuator limitation is related to the lateral force possible. Finally, the force allocation strategy involves the ability to control vehicle slip independently from vehicle yaw rate. This opportunity has been adapted in the ACM vehicle in order to relax vehicle slip from the original trajectory description. In such circumstances, the ACMs demonstrate better utilisation of the adhesion potential.

Keyword
autonomous corner module; force allocation; steering actuator; tyre constraints; vehicle control; vehicle dynamics
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-6772 (URN)10.1080/00423110701504215 (DOI)000257029700001 ()2-s2.0-46349108582 (Scopus ID)
Note
QC 20100629Available from: 2007-02-14 Created: 2007-02-14 Last updated: 2017-12-14Bibliographically approved

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